Microcapsules are typically composed of a liquid core and a solid shell which acts as a membrane separating the inner core from the outer environment. If the membrane is responsive to environmental conditions such as temperature, pressure, and/or pH, the microcapsules sense the condition and selectively release the encapsulants in the absence of external triggering. <br/>Gas hydrates are non-stoichiometric crystalline compounds which are formed by enclathrating gas molecules with hydrogen-bonded water molecules under high pressure and relatively low temperature conditions. In this study, we prepare microcapsules composed of a water core and polymeric shell using a microfluidic technique and investigate the effects of hydrate formation on the stability of microcapsules. The polymeric shell has a densely cross-linked network structure which interrupts mass transfer, allowing limited rates of diffusion for water and guest molecules. When the microcapsules containing water, exposed to the guest molecules methane and cyclopentane, are subjected to low temperature and high pressure, a hydrate is formed as water and the guest molecules are brought into contact in the shell. Upon hydrate formation, the tough polymeric shell becomes fractured. Moreover, the microcapsules are torn apart under shear stress in the presence of a hydrate layer on the surface. This shell fracturing entails the release of encapsulants from the microcapsules to the surrounding. We attribute the crack formation to the crystal growth in the narrow free volume of cross-linked network in the shell. The high driving force to form a gas hydrate overwhelms the ultimate strength of the network at the microscopic level, resulting in the shell fracturing. The hydrate-induced release of encapsulants is potentially useful for many applications. For example, the microcapsules can be used as smart carriers for hydrate inhibitors. If the inhibitors are released at the initial stage of hydrate formation, we can avoid a plugging in subsea flowlines which is hazardous and costly problem for offshore fields.

Hydrate formation in microcapsules for temperature-sensitive release of encapsulants

253rd National Meeting (2017)

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